Rolling mill control method and apparatus

ABSTRACT

Rolling mill with computer programmed for absolute lock-on AGC control rolls material having absolute aim gage without using an active thickness gage in the control loop. Computer is programmed to calculate; (a) lock-on length of rolled material, (b) mill stretch using a simplified subroutine, (c) calibration-corrected roll gap, (d) a lock-on thickness error relative to aim gage, (e) a corrected roll gap reference signal as a function of a constant lock-on thickness error and other variable thickness errors caused by changes in mill stretch and roll gap occurring after lock-on, and (f) a rate-sensitive variable gain of the corrected roll gap reference signal to reduce thickness errors to substantially zero as rapidly as possible.

United States Patent 11 1 I [111 3,906,764 Mueller Sept. 23, 1975 ROLLING MILL CONTROL METHOD AND APPARATUS I Primary Examiner-Milton S. Mehr [75] Inventor, George E Mueller Bethlehem Pa Attorney, Agent, or Firm-Joseph .I. OKeefe; John I.

' lverson; George G. Dower [73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa. [57] ABSTRACT Filed? 1974 Rolling mill with computer programmed for absolute [21] Appl No: 522,364 I lock-on AGC control rolls material having absolute aim gage without using an active thickness gage in the control loop. Computer is programmed to calculate;

U-S. Cl- (a) lock on length of rolled material, Stretch 1 72/21 using a simplified subroutine, (c) calibration- Int. GL o e t d roll gap a lock on thickness error rela.

of Search 7, 8, 9, l4, l9, tiv to aim gage a orre ted 1] gap reference ig- 72/20, 21 nal as a function of a constant lock-0n thickness error and other variable thickness errors caused by changes References Cited in mill stretch and roll gap occurring after lock-on, UNITED STATES PATENTS and (f) a rate-sensitive variable gain of the corrected 3,287,946 11/1966 Perrault et al. 72/8 r011 gap reference Signal to reduce thickness errors to 3,766,761 /1973 Adair et al 72/8 Substantially zero as rapidly as possible. 3,777,524 12 1973 Danehy et al 72/8 3,802,236 4/1975 Smith, Jr1 6! al. 72/16 Clams 3 Drawmg F'gures flGCCOR /4, amen/0am! ISCP 26 spa-0 JCQOQFZER 12 KEGULHTOR /24 r l 2/ E *1 nsau/n' Mm. A; Pl/LSE P0L$ 1 1 CE m 6 46C srksrcw scxswaomv R some 1 P 82 8 suaxaum: new ,wsM a 0 "1 EP 3251 F 2: g

1 l6 1 1 '3 L0 sMsc/v PSTfi/V 29 CE'LL PROCESSOR l I i /2 ,SCREW f Pas/rm PS /s v Aosr/z/v I I0 osrecroa 'g LP CC 5' 2; w \1 .g E \1 v Q Q Q Q i 23 37 22 Q LL g 5 z s LE/VG Tb mL/Bm'tT/a/v l3 PusewRREcT/M MILL SET-UP mm SOURCE SOURCE 5 OURCE US Patent Sept. 23,1975 Sheet 1 of 2 3,906,764

AGCCOR W /6. 5c sumo /v cp EED 5i M 1-1 REGULATOR /24 f2; 1 r ENTRY mop-our I g 3; MILL l A? PI/LSE PULSE 46a 5 STRETCH SCREWDOWN SOMQCE SOURCE P30228140! i k S 5 330 77 5 q MEcfl/i/v/s/w 5p 00/: m g 28 g l I r' Q K k F (o I /6 & H0 sMscM I LOAD F PST/WV 2 l CELL f PROCESSOR L0 fs I mam l I scnew :EL POSITION p5 1-L I ..BYY J DETECTOR Q g Q m \1 (I) Q T r LE/VG r// cnL/a/mr/a/v /3 PULSE COKREC 7/041 UP mm SOURCE sou/(m6 SOURCE Rqu. FORCE mosm MILL STKTC/l "P-STR/V" US Patent Sept. 23,1975 Sheet 2 on 3,906,764

j ROLLING ILL CONTROL METHOD AND APPARATUS BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates broadly to rolling mill control methods and apparatus. More particularly, this invention relates to rolling mill roll gap control methods and apparatus having an absolute lock-on AGC control system for rolling material to absolute aim gage. The term absolute lock-on AGC control system as used herein means a modified conventional lock-on automatic gage control system devoid of an active thickness gage in the control loop and one that rolls uniformly thick material after lock-on without the customary lock-on thickness error. The invention may be used in a reversing plate rolling'mill, as will be referred to herein, or in continuous rolling mills for rolling bars, sheet or strip and the like.

2. Description of the Prior Art Many rolling mills are equipped with computerdirected roll gap control systems. Control strategy includes setting roll gap initially to roll aim gage material using estimated values of both material properties and mill properties. In some instances after the material enters the mill rolls, the computer is programmed to direct a conventional lock-on AGC control system. That is, it locks on to head-end thickness and developes a corresponding roll gap reference signal that will cause a roll gap mechanism to maintain lock-on thickness uniformily along the length of material being rolled.

One major problem with a lock-on AGC control system in a reversing plate mill for example, is that the lock-on thickness of material exiting from rolls on a finishing stand is generally different for any given pass than the aim gage scheduled for that pass. Thickness errors occur in the roll gap reference signal because actual values of material properties at lock-on differ from the estimated values used to set roll gap initially. Such differences are attributable to locking-on the control system to a different gage material, a different temperature of material, a tapered or fish-tailed head-end, or over a furnace skidmark where the material is chilled locally. Any one or a combination of these situations may occur and each would require a different modification to the estimated values of roll force and mill stretch used to preset roll gap before lock-on. However, in conventional lock-on AGC control system only changes in roll force and mill stretch occuring after lock-on cause variations in the roll gap reference signal to maintain uniformity of lock-on material thickness.

Consequently, it has been discovered that considerable off-gage material is rolled having a lock-on thickness error.

In conventional lock-on AGC control system, a thickness gage located downstream of a mill strand is required in the control loop to continuously feed back thickness error signals tocompensate the roll gap reference signal for lock-on thickness errors. There are several drawbacks-to using the conventional lock-on AGC control system in a reversing plate mill. First, because of serious damage from cobbles and other hazards, therehas been no development for continuous thickness measuring gaging system with a gage located at the delivery ends of a finishing stand. Second, if a continuous thickness gaging system were available, the gage would have to be located a safe distance downstream of the mill stand, thereby increasing the transport time of the plate and thickness signal so that a low-gain in the feedback loop would be necessary to prevent loop instability. Third, many plate lengths tend to be short and the plate could be out of a mill stand before reaching a downstream thickness gage, thereby rendering lock-on thickness error compensation inoperative.

SUMMARY OF THE INVENTION One of the objects of this invention is to provide an improved method and apparatus for automatically controlling rolling mill roll gap to roll material having absolute aim gage.

Another of the objects of this invention is to provide an improved method and apparatus for automatically controlling rolling mill roll gap under a lock-on AGC control system which causes the production of rolled material devoid of lock-on thickness errors.

A further object of this invention is to provide a computer-directed method and apparatus for automatically controlling rolling mill roll gap with improved accuracy and speed of response.

The foregoing objects are attainable by a rolling mill roll gap control method and apparatus which includes a computer programmed for absolute lock-on AGC control without an active material thickness gage being used in the control loop. Absolute aim gage material is rolled by control means operatively associated with the computer and the computer program calculations include some or all of the following: (a) lock-on length of rolled material, (b) mill stretch using a simplified subroutine, (c) calibration-corrected roll gap spacing, (d) preferably a lock-on thickness error relative to aim gage, (e) preferably a corrected roll gap reference signal as a function of a constant lock-on thickness error and other variable errors caused by changes in mill stretch and roll gap occurring after lock-on, and (f) a rate-sensitive variable gain of the corrected roll gap reference signal to reduce thickness errors to substantially zero as rapidly as possible.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a reversing plate rolling mill having a computer-directed absolute lock-on AGC roll gap control embodiment of the present invention.

FIG. 2 is a flow diagram of a computer program for the computer shown in the FIG. 1 embodiment of the present invention.

FIG. 3 is a graph illustrating a family of roll force vs. mill stretch curves for a variety of plate widths (shown dotted) and a specific three-segment curve for a specific plate width and set of rolling conditions (shown solid).

- DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates diagrammatically plate material 10 being reduced in thickness in a conventional reversing plate rolling mill 11 between a pair of driven work rolls 12 and 13. Work roll 12 is moveable vertically to provide roll gap adjustment between it and fixed work roll 13.

Roll gap, as well as roll reducing forces, are controlled by screwdown speed regulator 14, the latter being responsive to either of two computer-directed signals as described below. Screwdown speed regulator 14 energizes screwdown mechanism 15 which in turn applies the roll forces through load cell 16 and work roll 12 to reduce the thickness of plate material 10. Load cell 16 output signal is roll force F signal which is fed to and processed in computer 17 as described below.

Initial roll gap is determined by screw position detector l8 measuring screw travel of screwdown mechanism 15. Detector 18 output signal is referred to hereinafter as screw position PS signal which is also fed to and processed in computer 17 as described below.

Computer 17 is preferably a general-purpose type having processor 19 which is adapted to receive the roll force F and screw position PS signals as well as other signals described below. Computer processor 19 includes conventional arithmetic, counting, general storage, specific storage to be described below and se quencing units to perform repetitive calculations at a cyclic frequency determined by computer clock 20. Computer 17 also includes absolute AGC program 21 which directs processor 19 operations to produce a signal that is fed to screwdown speed regulator 14. Absolute AGC program 21 is illustrated by the computer flow diagram shown in FIG. 2 and described below.

An additional group of computer 17 input signals are consolidated for ease of illustration and fed as mill setup data 22 to processor 19 to initiate either initial roll gap setting or automatic gage control operation. In practice, mill set-up data 22 may be derived from various sources such as a computer, a mill operator and/or a predetermined operating schedule. Such sources provide input data which are characterized with individual signals and fed to processor 19 as follows: (a) roll gap control by either manual or automatic gage control is the MAN/AGC signal; (b) aim gage of plate material for a given pass is the HAIM signal; (c) plate material 10 properties including known width and alloy or composition, and estimated values of mill entry thickness and temperature is the MATP signal; (d) plate mill 11 properties including roll diameter, roll crowns, roll material and mill spring constant is the MILP signal; (e) predicted roll force is the FPR signal; (F) initial roll gap set-up screw position is the ISCP reference signal; (g) desired length of plate material 10 beyond headend where lock-on AGC control takes over from initial roll gap set-up is the DLOL signal; and (h) predetermined constant of one or less selected to achieve the degree of absolute lock-on AGC control desired is the CMPLR signal.

Information concerning length of plate material 10 passing through mill stand 11 is initiated by coupling a well known rotary-pulse source 23 to work roll 13 and feeding length pulse LP signals to computer processor 19 for subsequent processing in relation to known diameterof work roll 13. Pulse processing begins when the head end of plate material 10 is detected entering work rolls 12 and 13 and causes a well known source 24 to feed an entry pulse EP signal to processor 19. The tail end of plate material 10 is detected leaving work rolls 12 and 13 by a well known source 25 which causes a drop'out pulse DOP signal to be fed to processor 19.

Computer 17 is equipped with a number of specific memory and storage devices which, as described below, are operatively associated with processor 19 and are provided in addition to those devices mentioned above. Lock-on memory device 26 temporarily stores a lock-on LO signal generated at the beginning of AGC control and is reset by the DOP signal. Mill stretch subroutine 27 contains preferably a tabular means for permanently storing a family of curves representing mill stretch versus roll force for a number of different plate material 10 properties and valid for a particular combination of mill properties as illustrated by dotted line curves in FIG. 3. Means are provided within subroutine 27 to correct the mill stretch calculations for combinations of the aforesaid mill properties other than those assumed in generating the stored table. When addressed with initial roll gap set-up values of FRP, MATP and MILP signals, processor 19 will cause mill stretch subroutine 27 to select and interpolate, if necessary, a set of specific mill stretch parameters SMSP having a constant nonlinear mill spring constant within an estimated roll force range equi-distant of the FPR signal. The SMSP parameters are stored temporarily in specific mill stretch curve memory device 28 where they characterize a specific three-segment mill stretch versus roll force F curve based on initial set-up conditions. This curve is shown by the solid line curve in FIG. 3 and identified by slopes M3, M4 and M5.

When roll force F signal is fed into memory device 28, a mill stretch PSTRN signal is produced at is output. Mill stretch memory device 29 temporarily stores the PSTRN signal in response to the LO signal and produces a lock-on mill stretch LOSTRN signal. A corrected screw position PSC signal is temporarily stored in screw position memory device 30 in response to the LO signal and produces a lock-on screw position LOSC signal. Both the LOSTRN and LOSC signals are used in subsequent calculations under AGC control operations. It is to be noted that memory devices 28, 29, and 30 are reset at the end of the LO signal.

OPERATION Referring now to FIGS. 1, 2 and 3, it will be assumed that initial roll gap is to be set up for a first pass of plate material 10 through reversing plate rolling mill 11 under manual operation of the roll gap control system. The MAN mode signal from data source 22 enables processor 19 to set-up manual roll gap control system while disabling the AGC control system. Ordinarily, processor 19 would direct the ISCP reference signal provided from data source 22 to screwdown speed regulator l4 and cause screwdown mechanism 15 to adjust roll gap until the PS signal is equal to the ISCP reference signal. When this would occur, the initial roll gap would be preset to equal aim gage rolled plate material 10 minus estimated mill stretch for a predicted value of roll force at lock-on.

However, it is preferred that computer 17 produce the ISCP reference signal during manual operation. This reference signal is produced simply by processor 19 directing the material and mill properties MATP and MILP signals, and the predicted roll force FPR signal, from data source 22 to mill stretch subroutine 27. Here a selection is made of specific mill stretch parameters SMSP which are represented by the solid threesegment curve in FIG. 3 and are fed to memory device 28 for the duration of a given pass as described above. Also, the initial value of predicted mill stretch PRDSTR signal is calculated and cause to occur at the output of memory device 28. Processor 19 directs the initial set-up value of the predicted PRDSTR signal to be substracted from the I-IAIMsignal supplied from data source 22 to produce the ISCP reference signal which is fed to screwdown speed controller 14. Screwdown mechanism then adjusts roll gap until screw position PS signal is equal to the ISCP reference signal, thereby establishing an initial roll gap set-up for plate mill 11.

It will now be assumed that the MAN mode signal supplied from data source 22 has been replaced with the AGC mode signal and processor 19 has enabled the absolute lock-on AGC control system and disabled the manual roll gap control system. Hereinafter, absolute AGC program 21 will direct processor 19 to' make changes in the initial roll gap set-up of plate mill 11.

Therefore, particular reference will now be made to FIG. 2.

PSTRN Si (F-Fi)/Mj, where (l) PSTRN instantaneous value of mill stretch during AGC control,

Si, Fi and Mj SMSP parameters stored in memory device 28.

Si mill stretch increment F roll force per signal Pi roll force increment Mj slope of mill spring constant which is shown by the solid curve in FIG. 3. The specific mill stretch parameters for the three-segment solid curve illustrated in FIG. 3 are F4, F5, S4, S5, M3, M4 and M5. For a given force F, the mill stretch corresponds to equation (2) as follows:

Many slabs requiring reduction in a plate mill have a head end that is tapered or fishtailed. In order to produce maximum yield of plate material 10 during rolling, one important factor to be developed is the exact point of lock-on for the AGC control system, That is, the point beyond the head end where full thickness and width of material 10 are being reduced by work rolls l2 and 13. Step 31 in computer program 21 calls for calculating the length of rolled material 10 once per pass by summing length pulses LP from source 23 with the onset of entry pulse HP from source 24. Step 32 calls for generating a lock-on LO signal once per pass when the sum of LP is equal to the desired lock-on length DLOL signal from data source 22. The value of the DLOL signal is predetermined in relation to the estimated current thickness and length and the accumulative reductions having been performed onplate material 10 thatis to enter plate mill 11. Step 32 also calls for storing the LO signal, in lock-on memory device 30, until reset by the occurance of the drop-out pulse DOP from source 25. Thus, lock-on AGC control is established when the LO signal is generated and AGC control is terminated when the DOP signal is generated as the tail end of plate material 10 passes through plate mill 11.

The next step in computer program 21 calls for step 33 to calculate a variable mill stretch PSTRN signal, this being done repetitively by starting with the onset of the LO signal and terminating at the end of the LO ,Signal. If during the above-described procedure of establishing the initial roll gap set-up the ISCP signal was derived from source 22, then the first cycle in the mill stretch calculation would be to perform the preferred method described above for addressing mill stretch subroutine 27 and storing the SMSP signals in memory device 28 for each pass. The second and subsequent cycles of calculating mill stretch would be performed ac cording to equation (1) below.

However, if the ISCP signal was obtained by the preferred method describedabove, then the SMSP signals would already be stored in memory device 28 for use during an entire pass. Therefore, the first and subsequent cycles in the mill stretch calculation in step 33 are to be performed by a simplified subroutine involving only roll force F and specific mill stretch parameter SMSP signals expressed as follows:

and M3, M4, and M5 are the slopes of the three segments in the solid curve shown in FIG. 3.

The simplified mill stretch subroutine carried out in step 33 is permissable on a repetitive basis for two reasons. First, the mill spring constant Mj is considered to be a nonlinear constant that does not change during a given pass as opposed to changeable constants dealt with in some prior art AGC control systems. Any changes that may occur in mil] housing dimensions during rolling, for example, are considered to be slowly varying linear changes, and if they do occur, are accounted for in corrected screw position PSC signal calculations described below. Second, there is no long computational procedure required on a repetitive basis to determine mill stretch PSTRN signals as are required in prior art AGC control systems.

In step 34 of computer program 21, the mill stretch PSTRN signal is stored once per pass in memory device 26 in response to the lock-on LO signal to produce a constant lock-on value of mill stretch LOSTRN signal for each pass of plate material 10 through mill 11.

i Itshould be observed that FIG. 3 shows a difference In computer program 21, step 35 calls for determin- 4 ing corrected roll gap by repetitively calculating a correct screw position PSC signal which is equal to adding a constant calibration correction CC signal to the variable screw position PC signal produced by detector 18. The constant CC signal is produced by calibration correction source 37. Source 37 may be an adjustable reference signal source set by a mill operator to account for slowly changing mill dimensions as well as observed thickness errors in rolled plate material 10 at the end of a given pass or series of passes. Constant thickness error data may also be supplied by nuclear gaging apparatus circuited outside of the absolute lock-on AGC control system. Such gages periodically gage plate material when at rest during a plate reversal between passes, stores a thickness error measurement while at rest, and then is returned off-line during movement of plate 10 through mill 11. Thus, the nuclear gaging apparatus does not play an active role in the lock-on AGC control system, but only measures and stores plate 10 thickness error at the end of any one or more passes of plate 10 through mill 11.

Step 38 calls for the corrected screw position PSC signal to be stored once per pass in memory device 30 in response to the lock-on LO signal to produce a constant lock-on screw position LOSC signal.

Step 39 calls for repetitively calculating a change in corrected screw position DSO signal which is equal to subtracting the LOSC signal from the PSC signal.

Step 40 in computer program 21 calls for a once per pass calculation of a plate material 10 constant lock-on thickness HLO signal, in response to the LO signal, which is equal to adding the LOSTRN signal stored in memory device 26 from step 34 to the LOSC signal stored in memory device 30 from step 38.

Step 41 calls for a once per pass calculation of a plate material 10 constant lock-on thickness error LODIFF signal, in response to the LO signal, which is equal to subtracting the HAIM signal provided by source 22 from the I-ILO signal produced in step 40. The LODIFF signal should correspond generally to the difference between the LOSTRN and predicted PRDSTR signals illustrated graphically in FIG. 3.

In order to provide the user with an adjustment in the degree of absolute lock-on AGC control desired, step 42 is provided in computer program 21 to call for a once per pass calculation of the percentage of absolute control CCADD signal. The CCADD signal is equal to multiplying the LODIFF signal produced in step 41 by the CMPLR signal provided by data source 22, the latter having a positive numerical value of one or less. If nothing less than 100% absolute lock-on AGC control is desired, then step 42 may be eliminated and computer program should advance to the next step.

Step 43 in computer program 21 is provided to call for repetitively calculating a corrected thicknes error DHO signal which will correspond to the corrected roll gap reference signal which eventially will become the second signal fed to regulator 14 as mentioned above. The DHO signal is equal to the sum of the change in screw position DSO signal produced in step 39, the change in mill stretch DSTRN signal produced in step 35, and the percentage of absolute control CCADD signal produced in step 42 if step 42 is used in computer program 21. Otherwise if step 42 is omitted, the LO- DIFF signal produced in step 41 should be substituted for the CCADD signal.

In order to achieve a rapid response to changes in the corrected thickness error DHO signal, and thereby maximize yield of rolled plate material 10, computer program 21 is provided with step 44 which calls for repetitively calculating a GAIN factor of the DHO signal. The GAIN factor is calculated in a conventional manner and is based on the rate of change in roll force F signal produced by load cell 16, the rate of change in screw position DSO signal produced in step 39, and the material properties MATP signal, the mill properties MILP signal and the aim gage l-IAIM signal, the latter three being fed from data source 22. The combined magnitude of these parameters determines the actual value of the GAIN factor.

Step 45 calls for the repetitive calculation of a corrected roll gap reference signal AGCCOR signal which is obtained by multiplying the corrected thickness error DHO signal produced in step 43 by the GAIN factor produced in step 44. The AGCCOR signal is fed to screwdown speed regulator 14 which causes screwdown mechanism 15 to continuously adjust roll gap to roll plate material 10 having absolute aim gage during operation of the absolute lock-on AGC control system.

When the tail end of plate material 10 exits from plate mill 11, the dropout DOP pulse terminates the lock-on LO signal, thereby terminating the absolute lock-on AGC control system.

I claim:

1. In a method of automatically con'rolling rolling mill roll gap where a preset roll gap is adjusted in response to a roll gap reference signal, the improvement which comprises:

a. establishing a lock-on AGC control mode when the head-end of said material enters the mill rolls, including:

l. storing lock-on values of mill stretch and roll position signals generated during rolling of said material, and

2. thereafter adjusting roll gap to maintain material thickness according to a roll gap reference signal which is produced in response to changes in said mill stretch and roll position signals after lockb. producing a lock-on thickness error signal by comparing an aim gage signal with said stored lock-on values of said mill stretch and roll position signals, and

c. correcting the roll gap reference signal by a predetermined amount of the lock-on thickness error signal to cause the production of rolled material having absolute aim gage.

2. The method of claim 1 wherein step (a) includes:

1. generating a lock-on control signal after a predetermined head-end length of material enters the mill rolls and initiating the storage of lock-on values of said signals in response thereto.

3. The method of claim 1 wherein step (a) includes:

2. calculating the mill stretch signal prior to lock-on as a function of a predicted roll force signal and a mill spring constant signal, the latter signal determined from plural signal sources representing various sets of operating parameters.

3. recalculating the mill stretch signal at lock-on as a function of an actual roll force signal and a stored specific mill spring constant signal determined from a specific signal source representing a given set of operating parameters at lock-on.

4. The method of claim 1 wherein the mill stretch signal of step (a) is calculated for each different pass of material through the mill.

5. The method of claim 1 wherein step (a) inclues;

4. modifying the roll position signal by a calibration correction signal produced by an external source.

6. The method of claim 5 wherein the calibration correction signal is produced by detecting changes in one or more stored signals representing predetermined rolling mill properties.

7. The method of claim 5 wherein the calibration correction signal is produced by detecting and storing a thickness signal derived from a gage devoid of the AGC control loop during one or more previous passes of material through the mill.

8. The method of claim 1 further including:

d. varying the gain of said roll gap reference signal to vary the speed of roll gap adjustment as a function one or more signals representing such parameters as material properties, and rate of change of roll force and roll position signals detected after lock- 9. A method of automatically controlling rolling mill roll gap to produce rolled material having absolute aim gage, which method comprises:

a. adjusting a screwdown mechanism to vary mill roll gap from an initial preset value to other values in response to a corrected screwdown reference signal,

b. establishing a lock-on AGC control mode when the head-end of said material enters the mill rolls, including storing lock-on values of mill stretch and roll position signals generated during rolling of said material, and thereafter adjusting the screwdown mechanism to maintain head-end material thickness according to a screwdown reference signal which is produced in response to changes in said mill stretch and roll position signals after lock-on,

c. producing a lock-on thickness error signal by comparing an aim gage signal with said stored lock-on values of said mill stretch and roll position signals, and

d. correcting the screwdown reference signal by a predetermined amount of the lock-on thickness error signal.

10. In apparatus for automatically controlling rolling mill roll gap where a preset roll gap is adjusted by means responsive to a roll gap reference signal, the improvement comprising:

a. means for producing a roll force signal,

b. means for producing a roll gap signal,

c. means for producing an aim gage signal,

d. computer means receiving said roll force, roll gap and aim gage signals and including:

1. programming means for establishing lock-on AGC control of roll gap,

2. means responsive to said roll force signal for producing a first signal representing a change in mill stretch after lock-on,

3. means responsive to said roll gap signal for producing a second signal representing a change in roll gap after lock-on,

4. means responsive to said aim gage signal lock-on values of mill stretch and roll gap signals for producing a third signal representing a lock-on thickness error function, and

5. means responsive to said first, second and third signals for producing a corrected roll gap reference which acts on said adjusting means to cause production of rolled material having absolute aim gage.

11 The apparatus of claim 10 including:

e. means for generating a lock-on control signal after a predetermined head-end length of material enters the mill rolls and controlling the storage of lock-on values of said mill stretch and roll force signals with said lock-on control signal.

12. The apparatus of claim 10 including:

f. means for producing a predicted roll force signal and plural signals representing various sets of operating parameters, and wherein computer means ((1) includes:

21. means for storing a family of mill stretch curves,

22. means for storing a specific mill stretch curve, said 1 means programmed for computer means (d) to cause said 21 means to receive said means (f) signals prior to lock-on and to select a specific mill stretch curve in response thereto, and to store said selection in means 22, and said 1 means also programmed for computer means ((1) to calculate mill stretch after lock-on as a function of the specific mill stretch curve stored in means 22 and the actual roll force signal of means (a).

13. The apparatus of claim wherein computer means (d) is programmed by means 1 to calculate mill stretch for each different pass of material through said rolling mill.

14. The apparatus of claim 1 including:

g. means for producing a calibration correction signal, said signal modifying the roll gap signal in computer means d3 to provide a corrected second signal.

15. The apparatus of claim 1 including:

h. means for producing plural signals of corresponding plural operating parameters, and wherein computer means (d) further includes:

6. means receiving said means (a) signal, said means d3 second signal, and said means (h) signals for varying the gain of said means d5 corrected roll gap reference signal to vary the speed of roll gap adjustment as a function of one or more of said means (h) signals and the rate of change of said means (a) and d3 signals.

16. Apparatus for automatically controlling rolling mill roll gap to produce rolled material having absolute 40 aim gage, comprising:

a. means including a screwdown mechanism for adjusting mill roll gap from an initial preset value to other values in response to a corrected roll gap reference signal,

b. means for producing a roll force signal,

c. means for producing a screw position signal,

01. means for producing an aim gage signal,

e. computer means receiving said roll force, screw position and aim gage signals and including:

50 1. programming means for establishing lock-on AGC control of roll gap,

2. means responsive to said roll force signal for producing a first signal representing a change in mill stretch after lock-on,

3. means responsive to said screw position signal for producing a second signal representing a change in screw position after lock-on,

4. means responsive to said aim gage signal and lock-on values of mill stretch and screw position signals for producing a third signal representing a lock-on thickness error function, and

5. means responsive to said first, second and third signals for producing a corrected roll gap reference which acts on said adjusting means. 65 l 

1. In a method of automatically controlling rolling mill roll gap where a preset roll gap is adjusted in response to a roll gap reference signal, the improvement which comprises: a. establishing a lock-on AGC control mode when the head-end of said material enters the mill rolls, including:
 1. storing lock-on values of mill stretch and roll position signals generated during rolling of said material, and
 2. thereafter adjusting roll gap to maintain material thickness according to a roll gap reference signal which is produced in response to changes in said mill stretch and roll position signals after lock-on, b. producing a lock-on thickness error signal by comparing an aim gage signal with said stored lock-on values of said mill stretch and roll position signals, and c. correcting the roll gap reference signal by a predetermined amount of the lock-on thickness error signal to cause the production of rolled material having absolute aim gage.
 2. thereafter adjusting roll gap to maintain material thickness according to a roll gap reference signal which is produced in response to changes in said mill stretch and roll position signals after lock-on, b. producing a lock-on thickness error signal by comparing an aim gage signal with said stored lock-on values of said mill stretch and roll position signals, and c. correcting the roll gap reference signal by a predetermined amount of the lock-on thickness error signal to cause the production of rolled material having absolute aim gage.
 2. The method of claim 1 wherein step (a) includes:
 2. calculating the mill stretch signal prior to lock-on as a function of a predicted roll force signal and a mill spring constant signal, the latter signal determined from plural signal sources representing various sets of operating parameters.
 2. means responsive to said roll force signal for producing a first signal representing a change in mill stretch after lock-on,
 2. means responsive to said roll force signal for producing a first signal representing a change in mill stretch after lock-on,
 3. means responsive to said roll gap signal for producing a second signal representing a change in roll gap after lock-on,
 3. means responsive to said screw position signal for producing a second signal representing a change in screw position after lock-on,
 3. recalculating the mill stretch signal at lock-on as a function of an actual roll force signal and a stored specific mill spring constant signal determined from a specific signal source representing a given set of operating parameters at lock-on.
 3. The method of claim 1 wherein step (a) includes:
 4. The method of claim 1 wherein the mill stretch signal of step (a) is calculated for each different pass of material through the mill.
 4. means responsive to said aim gage signal and lock-on values of mill stretch and screw position signals for producing a third signal representing a lock-on thickness error function, and
 4. modifying the roll position signal by a calibration correction signal produced by an external source.
 4. means responsive to said aim gage signal lock-on values of mill stretch and roll gap signals for producing a third signal representing a lock-on thickness error function, and
 5. means responsive to said first, second and third signals for producing a corrected roll gap reference which acts on said adjusting means to cause production of rolled material having absolute aim gage.
 5. means responsive to said first, second and third signals for producing a corrected roll gap reference which acts on said adjusting means.
 5. The method of claim 1 wherein step (a) inclues;
 6. The method of claim 5 wherein the calibration correction signal is produced by detecting changes in one or more stored signals representing predetermined rolling mill properties.
 6. means receiving said means (a) signal, said means d3 second signal, and said means (h) signals for varying the gain of said means d5 corrected roll gap reference signal to vary the speed of roll gap adjustment as a function of one or more of said means (h) signals and the rate of change of said means (a) and d3 signals.
 7. The method of claim 5 wherein The calibration correction signal is produced by detecting and storing a thickness signal derived from a gage devoid of the AGC control loop during one or more previous passes of material through the mill.
 8. The method of claim 1 further including: d. varying the gain of said roll gap reference signal to vary the speed of roll gap adjustment as a function one or more signals representing such parameters as material properties, and rate of change of roll force and roll position signals detected after lock-on.
 9. A method of automatically controlling rolling mill roll gap to produce rolled material having absolute aim gage, which method comprises: a. adjusting a screwdown mechanism to vary mill roll gap from an initial preset value to other values in response to a corrected screwdown reference signal, b. establishing a lock-on AGC control mode when the head-end of said material enters the mill rolls, including storing lock-on values of mill stretch and roll position signals generated during rolling of said material, and thereafter adjusting the screwdown mechanism to maintain head-end material thickness according to a screwdown reference signal which is produced in response to changes in said mill stretch and roll position signals after lock-on, c. producing a lock-on thickness error signal by comparing an aim gage signal with said stored lock-on values of said mill stretch and roll position signals, and d. correcting the screwdown reference signal by a predetermined amount of the lock-on thickness error signal.
 10. In apparatus for automatically controlling rolling mill roll gap where a preset roll gap is adjusted by means responsive to a roll gap reference signal, the improvement comprising: a. means for producing a roll force signal, b. means for producing a roll gap signal, c. means for producing an aim gage signal, d. computer means receiving said roll force, roll gap and aim gage signals and including:
 11. The apparatus of claim 10 including: e. means for generating a lock-on control signal after a predetermined head-end length of material enters the mill rolls and controlling the storage of lock-on values of said mill stretch and roll force signals with said lock-on control signal.
 12. The apparatus of claim 10 including: f. means for producing a predicted roll force signal and plural signals representing various sets of operating parameters, and wherein computer means (d) includes:
 13. The apparatus of claim 10 wherein computer means (d) is programmed by means 1 to calculate mill stretch for each different pass of material through said rolling miLl.
 14. The apparatus of claim 1 including: g. means for producing a calibration correction signal, said signal modifying the roll gap signal in computer means d3 to provide a corrected second signal.
 15. The apparatus of claim 1 including: h. means for producing plural signals of corresponding plural operating parameters, and wherein computer means (d) further includes:
 16. Apparatus for automatically controlling rolling mill roll gap to produce rolled material having absolute aim gage, comprising: a. means including a screwdown mechanism for adjusting mill roll gap from an initial preset value to other values in response to a corrected roll gap reference signal, b. means for producing a roll force signal, c. means for producing a screw position signal, d. means for producing an aim gage signal, e. computer means receiving said roll force, screw position and aim gage signals and including:
 21. means for storing a family of mill stretch curves,
 22. means for storing a specific mill stretch curve, said 1 means programmed for computer means (d) to cause said 21 means to receive said means (f) signals prior to lock-on and to select a specific mill stretch curve in response thereto, and to store said selection in means 22, and said 1 means also programmed for computer means (d) to calculate mill stretch after lock-on as a function of the specific mill stretch curve stored in means 22 and the actual roll force signal of means (a). 